Prevention of corrosion in furfural rerun systems



Feb. 25, 1947.- v. SCARTH PREVENTION OF CORROSION IN FURFURAL RERUN SYSTEMS Filed July 26, 1945 2' s L; l 3 S h. D: m l: D g i im 'www 2 @a hllhlllc Nw oNuvavdas I |I I Il Illlllllll'll ,|I l|||||||||||l n N -l f o HIV L uz-lddlals l l 'I `o Il N t I l N O N l N .f1 aolvaodvAa l I.: niemand i I' l Q l l l l v l l 9 Q/ i \t a ."z/

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Patented Feb. 25, 1947 ?REVENTION OF CORROSION IN FURFURAL RERUN SYSTEMSv Virgil Scarth, Bartlesville, Okla., assigner to Phillips Petroleum Company,y a corporation oi" Delaware Application July 26, 1945, Serial No. 607;,212

9 Claims. 1

This invention relates to chemical treatment of furfural in distillation systems used for purification of furfural. In one particular aspect it relates to a method for substantial elimination of corrosiveness in furfural in rerun units of; eX- tractive distillation processes and in another particular aspect it relates to a method for inhibitn ing polymerization of -furiuial in rerun units of extractive distillation systems.

Furfural has found wide use as a solvent in extractive distillation processes because of its property of selective absorption for unsaturated It is especially usefull in separating butadiene and/or other unsaturated aliphatic hydrocarbons from admixture with saturated hydrocarbons of similar boiling range by extractive distillation. Principal disadvantages to the use of furfural in such processes are the formation of polymers in the furfural during such use and the development of extreme corrosiveness toward carbon steel equipment.

The nature and origin of the corrosive mate rials in such furfural is not understood. Since the furfural becomes more acid during such use numerous attempts to correlate the corrosiveness of such furfural with its acid content have been made but without success. Furfural withdrawn from circulating streams in such processes and foundto have an acid content of only 0.04% have been found to be very corrosive, whereas other samples of furfural so withdrawn from such process streams have been found to bench-corrosive although their acid content was 0.06%. It is evident that the corrosiveness of furfural which has been used in extractive distillation processes for the. separation of unsaturatedhydrocarbon. from mixed hydrocarbon streams is `due to corrosive materials other than acids. It is not known Whether these corrosive materials enter the system as impurities in the hydrocarbon stream and are extracted 'therefrom by thek furfural, or develop during the extractive distillation process either by reaction between the furfural solvent and 'some material in the hydrocarbon stream or develop in the furfural itself. Furthermore corrosion of equipment handling such furfural is not evenly distributed but is localized at points where the velocity of the furfural stream is relatively high; constrictions, motor valves, pump impellers, heat exchangers, etc., being'especially attacked While tanks, straight piping, fractionating towers and similar equipment are little affected. The corrosive materials apparently become concentrated in the furfural redistillation unity vand severe corrosion ofl this unit` results, @Replace ment of corroded parts is a major equipment expense in extractiva distillation plants using furfural as solvent. f

The cause of polymer formation in such furfural` is not Well understood although ity is believed that heat, pressure, high Water content of the furfural, the presence of unsaturated hydrocarbons, air or oxygen, and high furfural polymer content are conducive to their formation. When the polymer content of the furfural i-n such systems becomes high polymers accumulate on and coat heating elements, coking and interfering lwith heat transfer. High furfural polymer content also causes fouling and plugging of piping and raises the boiling pointof the furfural in the system as well as decreases the eiiiciency of the furfural as a selective solvent for unsaturates.

It is therefore necessary to redistill such fur--` fural at intervals in order to maintain low poly.- mer content. Severer corrosion of the distillation equipment in the purification unit results.

It is an object of my invention to provide a method of chemical treatment of the furfural in such purication units which will substantially eliminate corrosion therein.

Another object of my invention is to provide a method of chemical treatment of furfural which will inhibit Vpolymer formation in such purification units.

Ano-ther object of my invention, is to prevent foaming of furiural during distillation in repurification units.

Numerous other objects and features of novelty will become apparent to those skilled in the` art upon reference to the accompanying drawing which shows diagrarmnatically one illustrative embodiment of my invention. y I have found that the continuous, controlled addition of lime to the cold, incoming furfural feed to the rerun unit results inthe substantial elimination of corrosion in said rerun unit, inhibits polymer formation in said unit and yields a furfural distillate which is non-corrosive until new corrosive material develops therein during use. This lime may be added to the cold furfural either as an aqueous solution, aqueous dispersion or as a dispersion in furfural or as a dry powder. The lime so added may be either calcium hydroxide or calcium oxide. Relative coolness of the furfural stream at the point of addition of such lime is a necessary condition for obtaining best results, because it is very diicultto avoid the formation of small local areas of eX- cess alkalinity in the furfural during such addition; oflime.; `Such areasof.localexcess[alkalinity formation when furfural is at or near its boiling 1 point but have no noticeable effect when the furfural is relatively cool, i. e., at a temperature from that about 40 F. to 140 F. Lime may be added` directlyrtov the boiling furfural in the still and when so added will inhibit corrosion but will increase the rate of polymer formation.

The reason why such addition of lime to the incoming furfural feed prevents corrosion of the rerun equipment and inhibits polymer formation is not well understood but it is known that the reaction is not a simple neutralization of the acids contained in such furfural. Thisris borne out by the fact that I have obtained best results when the quantity of lime added to the furfural feed is from 2 to 4 times the quantity sufficient to neutralize the acidity of the furfural; and by the fact that attempts to neutralize Isuch acids by addition of alkali hydroxides have been made but f have uniformly given very poor results and have been found to be impractical for such use. Attempts to use carbonates for the purpose of neutralizing the acidity of such furfural have resulted in troublesome foaming and great difficulties in operation due to such foaming. Such dimculties are avoided by the use of my invention.

Since the corrosiveness of such furfural is not dependent upon its acid content it is probable that the corrosive material present either combines'with lime and loses its property of corrosiveness, or that such'material requires the presence of acid for its activation; but I do not know this to be true and do not wish to limit my invention to any theory or mechanism of chemical action.

The' operation of my invention may be better understood by reference to the accompanying drawing which shows diagrammatically one illustrative embodiment of this invention.

Cooled', used furfural from the extractive distillation process enters the puricationunit via line l and is conducted to the mixing chamber2.

At or near the mixing chamber 2, lime, in aqueous Y solution or dispersion, is added to said furfural Vcontinuously and at a rate such that vthe duan-V Vtity of lime so introduced is from 2 to 4 times the Yquantity required to neutralize the acidity of the furfural feed and is preferably about three times that quantity. Mixing chamberY 2 is equipped with a conventional means for intimately fmixing the lime and furfural feed. The mixture is then conducted via line 4 to the middle portion of a furfural evaporator 5, where the incoming stream is met by ascending hot furfural vapor and steam. The overhead vapors are conducted via line 8 to condenser Vi0 and the condensate from condenser i is lead through line Il to the settling vtank l2 where said condensate is allowed toV separate into an aqueouslayer and a furfural layer. Puried, non-corrosive furfural is withdrawn from the bottom of settling tank I2 and returned Ato the extractive distillation process. Water saturated with furfural is withdrawn from the aqueous layer in'settling tank l2 vial line |14 and may be advantageously used as feed water for a boiler wherein steamj is generated and introduced via line for the steam distillation of furfural. v f

Y'Ihe'kettle product from evaporator 5, contain- Y ing furfural, furfural polymers, calcium compounds and high boiling materials, is withdrawn by line il and introduced into the middleportion of a second furfural evaporatorv I8 where the dey-- scending liquid feed is again met by a rising cury tion subsequent to the use of said furfural in an Y 4 rent of hot furfural vapors and steam. Overhead vapors from evaporator I8 are conducted via line i9 to the bottom portion of evaporator 5 and are p introduced therein through openings in line 20 inside evaporator 5.

The kettle product from evaporator I8 is Withdrawn via line 22 and is introduced into the mid portion of stripper column 23. In this column the descending liquid feed encounters an ascend-1 ing current of steam introduced into the bottom of column 23 via line 25 and is stripped of its remaining furfural content. The kettle product of column 23, consisting essentially of furfural polymer, together with some lime compounds and high boiling impurities is withdrawn via line 25 and in the absence of any use therefor may conveniently be conducted to'pits for burning.

In my Patent No. 2,404,253, issued July 16, 1946, I have disclosed the addition of lime to the furfural in the main furfural process streams of extractive distillation plants wherein unsaturated aliphatic hydrocarbons are separated from a mixed hydrocarbon stream containing them, but such addition of lime while substantially eliminating corrosion in the main extractiva distillation system is not suicient to prevent severe corrosion of rerun equipment, wherein the corrosive materials apparently become concentrated. 'Io` prevent corrosion in rerun units addition of lime far in excess of the amount necessary to neutralize the acidity of the incoming furfural is required. I have found that lime may be added in suchV excess with decrease in the rate of polymer formation. Y

' Example In an extractive distillation plant for the manufacture of butadiene wherein unsaturated aliphatic hydrocarbons were separated from mixed hydrocarbon streams containing them by theuse of furfural asV solvent the furfural conand had-,an acid content of 0.04%Y calculated as Y acetic acid and a polymer content of 0.33%. Furfural lost by withdrawing via line 25 was 1,500 gallons per day. This Waste product so withdrawn consisted essentially of furfural polymers in admixture with sufficient residual furfural to give fluidity to the mixture. Under such operating conditions severe corrosion of the rerun vunit resulted. Mixing chamber 2 was installed and an aqueous dispersion of lime was introduced via line 3 at a rate of l2 pounds of calcium hydroxide per hour while the rerun unit was otherwise operated as before. Corrosion of the rerun unit was substantially eliminated and loss of furfural by withdrawal via line 25 was reducedto 1,200 gallons per day.

Having described my invention and the operation thereof, I claim: i

l. In the art of purifying furfural by redistillaextractive distillation process for the separation of unsaturated aliphatic hydrocarbons fromj a,

mixed 'hydrocarbon stream containing such unsaturates, that improvement which consists of continuously withdrawing a stream ofused'furfural from such extractive distillation process; maintaining such furfural. so withdrawn within the temperature range of to 130 Ffwh'ile continuously adding lime kthereto at a rate of from two to four times the quantity of lime required to neutralize the acids contained in such furfural, intimately mixing said lime so added with said furfural, introducing the resulting mixture into an evaporator, evaporating said furfural in the presence of steam, withdrawingoverhead vapors of furfural and water, condensing such overhead vapors, separating excess water from the condensate by separation of aqueous and furfural layers, returning purified furfural from the bottom layer to the extractive distillation process and withdrawing a kettle product comprising furfural, furfural polymers, lime compounds and high boiling impurities from said evaporator.

2. The process of claim 1 wherein furfural is maintained in the temperature range of 40 to 140 F. while lime is added.

3. In the art of extractive distillation of hydrocarbons wherein furfural is used as selective solvent, that improvement which consists of preventing corrosion of furfural rerun units and polymerization of furfural therein by feeding used furfural from the extractive distillation process to such rerun units continuously; maintaining the temperature of the furfural so fed within the temperature range of 120 to 130 F. while adding lime continuously thereto at controlled rate whereby the amount of lime so added is three times the quantity necessary for the neutralization of the acidity of the furfural feed intimately mixing the lime so added with the furfural feed; continuously introducing the resulting mixture into distillation equipment and therein steam distilling said mixture, withdrawing overhead va- 6. In the operation of a furfural puriiicationI system which contains a furfural evaporator arfurfural, received from an extractive distillation.` v

process wherein said furfural was used as selective solvent for the separation of unsaturated aliphatic hydrocarbons from a mixed hydrocarbon stream, at a temperature of to 130 F. while continuously adding lime thereto; controlling the rate of addition of lime so that the quantity added will be about three times the amount necessary for neutralizing the acidity of said furfural; intimately mixing the lime so added with the furfural and continuously feeding the resulting mixture to said furfural evaporator.

7. The process of claim 6 wherein the furfural is maintained in the temperature range from 40 to F. while lime is added.

8. The process of claim 6 wherein' the amount of lime added to the furfural is from ytwo to four times the quantity required to neutralize the acidity of the furiural.

9. In the operation of a furfural rerun unit wherein furfural which has been used as selective solvent for separating unsaturated aliphatic hydrocarbons from a mixture 0f hydrocarbons containing the same by extractive distillation is repuriiied by distillation, that improvement which comprises adding lime to such furfural to be distilled `and controlling the quantity of lime so addedin the range from two to four times the quantity required to neutralize the acidity of said furfural. i

VIRGIL SCARTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

